1. Field of the Invention
This invention relates to the electrohydrodynamic generation of sub-micron to micron size particles, to the rapid cooling and solidification of such particles, the preparation of amorphous metals, alloys, ceramics and the like from such particles, the application of thin film coatings from such particles, and the apparatus for electrohydrodynamically generating the sub-micron to micron size particles and for carrying out the rapid cooling and solidification and thin film coating applications as well as other applications.
2. Discussion of the Prior Art
The production of fine metal powders has been an active field of technology and many different approaches have been taken for the production of these metal as well as non-metal particles. For example, in U.S. Pat. No. 3,830,603 to Blucher, et al. the patentees mention many prior art techniques such as the atomization of molten metal by gas jets or by high pressure water; spraying molten metal into a vacuum to form discrete particles; the vaporization of metal in a vacuum followed by condensation; the fusion of metal by an electric arc followed by the formation of condensed droplets which may be forced out of the arc zone either by means of a gas stream or by centrifugal force either alone or coupled with the influence of the magnetic repulsion inherent in the arc; forming a molten surface on a metal rod and agitating the molten metal at ultrasonic frequency generated either by an ultrasonic transducer or by use of a high frequency electric current coupled with a strong direct current magnetic field. The processes of these prior art references are carried on either in the presence of an inert gas or in a vacuum. The Blucher, et al. apparatus produces fine metal powder from a wire or rod by forming particles of molten metal in an electric arc and removing the formed particles by the interaction of two magnetic fields operating at right angles to one another.
While these devices have achieved some degree of success, there is still a need for a more efficient means of obtaining even finer size particles from a broader range of materials than can be accomplished by any of the above mentioned techniques.
It has been possible by electrohydrodynamic spraying techniques to produce singly charged ions and heavier sub-micron particles as described, for example, by Swatik and Hendricks, "Production of Ions by Electrohydrodynamic Spraying Techniques" J. AIAA, Vol. 6, 1596-7 (August 1968); Mahoney, et al., "Electrohydrodynamic Ion Source", J. Applied Physics, Vol. 40, 5101-06, (December 1969). However, the electrohydrodynamic (EHD) spraying technique has principally been used only as a research tool for testing properties of singly charged and multiply charged ions and as an electric propulsion source. The full potential for the electrohydrodynamic spraying technique for forming new types of materials and ultra-fine particles has neither been fully appreciated nor developed to the extent where the potential applications of this technique could be applied in a commercially useful sense.
In particular, it has now been found that electrohydrodynamic spraying can be used to form sub-micron to micron size particles from metal alloys, ceramic materials and similar high melting point composite materials which never previously existed in that form. It has also been discovered that very thin coatings having superior properties can be formed from such materials.